Monday Night's Supermoon Will Be The Biggest In A Century

As night sets in on November 14, wander outside and gawk at the sky. If the weather is clear, the moon will be at its biggest and brightest in nearly 70 years, and it won't put on a similar display until late 2034, astronomers say.

A so-called "supermoon" occurs when the moon is not only full, but is orbiting close to Earth. This month's full moon will be the closest to Earth since January 26, 1948.

NASA says a supermoon - technically called a perigee moon - can appear to be as much as 14 per cent bigger and 30 per cent brighter than a full moon at its furthest orbital point.

A supermoon rises over Canberra in 2014. Photo: Fadli Rozi

But NASA says the November 14 moon could, arguably, even be called an "extra-supermoon", and here's why.

Since the moon has an elliptical orbit, one side of the orbit (the perigee) is about 48,000 kilometres closer to Earth than the other side (the apogee). When the Earth, moon and sun line up in an orbit, while the moon is on its nearest approach to Earth, we are treated to a so-called supermoon.

This happens three times this year: on October 16, November 14 and on December 14. But, on the middle date, the moon becomes full just two hours after its closest approach to Earth.

"On November 14, it becomes full within about two hours of perigee - arguably making it an extra-supermoon," NASA says.

"The full moon of November 14 is not only the closest full moon of 2016 but also the closest full moon to date in the 21st century. The full moon won't come this close to Earth again until November 25, 2034."

While the moon would look spectacular on the night, Perry Vlahos, the vice-president of the Astronomical Society of Victoria, said stargazers would probably not notice any difference between the three supermoons this year.

"The difference between other close moons would only be, in some instances, 100, 200 or 300 kilometres. To the human eye, that is almost imperceptible from a distance as great as that," he said.

But he said that many people never watched the moon rise. Low-hanging moons could create what was known as a moon illusion: when the moon appears unusually large while coming over the horizon.

He advised those wanting to watch the supermoon rise on November 14 to head at dusk to an east-facing beach, or to the top of a hill or mountain with uninterrupted views to the east.

"In Sydney, any of the beaches facing towards the east, like Manly or Bondi, would be good. In Melbourne, it would be a beach on the western side of Port Phillip Bay," he said.

"If you're in the city, get on top of the highest building that you can."

Weatherzone said the date was too far away to forecast what the weather and cloud cover would be like on the night.

This article originally appeared in Digital Life, The Sydney Morning Herald's home for everything technology. Follow Digital Life on Facebook and Twitter.

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